The present invention relates to an ophthalmologic apparatus, according to the preamble of claim 1.
Optical coherence tomography (OCT) is an established noninvasive, noncontact imaging technology which can image eye structures, and more importantly high resolution cross sectional images of the retina not only on the surface, but also up to certain depth are produced. Basics of this method is available on the internet (e.g. in the Wikipedia).
An apparatus and a method for diagnosing and monitoring eye diseases by OCT is described in U.S. Pat. No. 6,293,674. U.S. Pat. No. 6,325,512 proposes to perform relatively slow OCT scans to obtain a high signal-to-noise ratio. Eye movements during the scan are compensated by a tracking system. The tracking system uses a point photo detector and a dithering light path for scanning a certain region around a distinct point of the retina (particularly more reflective, darker etc.). Any movement out of the center of the scanned region is registered and accused to adjust mirrors in the general light path of the instrument to compensate for this movement, i.e. a movement of the eye. Obviously, this provision requires fast reacting and exact working mechanical means, hence is prone to wear and sensitive to mechanical effects (shock, vibration).
An OCT apparatus of improved vision and resolution of retinal images is presented by U.S. Pat. No. 6,379,005. The distortion of the eye is determined by observing a laser light spot on the retina using a Hartmann-Shack wavefront sensor and compensating the aberration using e.g. a deformable mirror.
This patent still contains an extensive list of patent and non-patent prior art.
All the known and described apparatuses are designed to be used by professionals and are stationary. In consequence, to begin an examination, the OCT apparatus has to be adjusted to the properties of the eye (myopic, hyperopic).
Furthermore, the professional (e.g. ophthalmologist) has to search manually a region of interest which is to be observed more closely.
OCT has proven to be a precious diagnostic tool for e.g. glaucoma, vitreo-retinal-disorders or AMD (age-related macular disease). In the latter case, OCT may not only be useful to determine the extent of the concerned region of the retina, but also to aim a laser to the correct target region for therapy.
A disadvantage of the known apparatuses is that they have to be adjusted to each patient and that the ophthalmologist or a well instructed expert has each time to search for the region of interest and to perform the corresponding adjustments manually.
Another aspect is that in many cases, the state of the eyes of a patient, and more particularly one or more distinct “regions of interest” (ROI), have to be examined regularly in order to determine as early as possible a change thereof. However, due to the fact that the patient has to visit a professional therefor, it was impossible to perform the examinations as often as desirable.
US-A-2006/0187462 discloses an automatic method of obtaining OCT images of the retina. The OCT device first performs linear survey OCT scans. Each such scan consists of two linear scans yielding each a cross-section of the retina oriented about orthogonally with respect to each other. From the position of a characteristic land mark feature in the images, a correction of the orientation of the device is calculated to center it on the land mark. Generally, due to irregularities of the eye, this procedure has to be performed more than once to achieve an exact aiming of the device. Then the actual OCT image is taken.
The survey scans are performed sufficiently rapidly that a misalignment due to eye movements is avoided.
This approach requires a particular design of the OCT unit to allow high precision and survey scans, and algorithms for rapid evaluation of the survey scans.